1. Field of the Invention
This invention relates generally to wireless networks. More particularly, this invention relates to communication protocols that are suitable for wireless mesh networks.
2. Description of the Related Art
The appetite for information continues to grow the Internet. Because of such growth new information is constantly being added, which fuels even more growth. Such growth has caused bandwidth problems in many areas. Indeed, yesteryear's limited bandwidth telephone dial-up services are rapidly being replaced with broad bandwidth systems such as digital subscriber lines (DSL) and cable modems. Unfortunately, such systems are not available to a significant portion of the population. Moreover, the acquisition and installation costs associated with such systems make them unappealing to some users and to some service providers.
An alternative to wired communication systems is wireless communications. Wireless communication systems can be deployed very rapidly and at less cost than its wired counterparts. Wireless communication systems that use cellular phone technologies are becoming commonplace, primarily because they provide mobile Internet connectivity. Unfortunately, most cellular phone systems tend to be severely bandwidth limited.
A wireless communication system that can provide a bandwidth comparable to DSL and cable modem technologies, but that is less difficult and costly to install, uses a mesh network. As described in U.S. patent application Ser. No. 10/122,886, filed Apr. 15, 2002 and in U.S. patent application Ser. No. 10/122,762, filed Apr. 15, 2002, which are incorporated herein by reference, such a mesh network comprises a plurality of wirelessly connected nodes that communicate information traffic across a wide area. The individual nodes of the mesh network communicate using radio or microwave signals to pass information between a Mesh Gateway and Customer Premise Equipment (CPE). The Mesh Gateway itself is coupled to the remainder of the Internet, for example by a cable or by an optical fiber, while the CPEs are connected to the mesh network using roof mounted, multidirectional antennas. Those antennas implement an antenna array technology that provides for selectively switched directionality. Such roof top directional antennas can be directed in different directions and are very effective in connecting to neighboring nodes, which are described in more detail subsequently.
Mesh nodes with multiple directional antennas pose a problem. Both ends of a mesh communication link need to be using appropriate antennas or the link will not close. When multiple antennas are possible in each node, a mechanism to coordinate the communications is needed. Internet communication protocols for wireless and wired communications often use the IEEE 802.11 standard family of protocols. While these protocols are usually asynchronous using a distributed coordination function (DCF), an alternative point coordination function (PCF) is an option. The PCF is based on a polling technique wherein a network coordinating station polls other network nodes that the network coordinating station knows are connected to the network. To do so, the network coordinating station sends a beacon to all the network nodes within its transmission range announcing the beginning of a polling sequence. The network coordinating station then sequentially polls each network node, either delivering information to that node or requesting information from that node. The network nodes acknowledge being polled and then receive or send information to the coordinating station. Acknowledgement is typically performed in subsequent polling sequences.
Of course, the foregoing requires that the network coordinating station knows what other network nodes are within its transmission range. To obtain this information, a distributor coordination function (DCF) protocol found within the IEEE 802.11b protocol is used. DCF provides a controlled method of finding new entrants into the network, thus allow the PCF to operate for as long as one wants to poll. In practice, PCF polling can deliver nearly isochronous traffic.
To coordinate polling, a single station is assigned the role of polling coordinator (PC). The PC coordinates polling of various stations within reach of a network node.
While useful in many applications, a PCF and a PC in accord with the IEEE 802.11 protocol family may not be useful in many applications. For example, the IEEE 802.11 PCF function finds limited use in a wireless mesh network architecture where multiple nodes must coordinate polling. Such distributed polling coordination is not supported by the 802.11 protocol, but is necessary for mesh network functionality. Therefore, there is a need for a communication protocol that facilitates polling coordination distribution.